This invention relates to an integrated circuit (IC) testing apparatus, and more particularly to the construction of an IC socket onto which semiconductor devices being tested (ICs being tested) are to be placed for electrical connection and which is superior in the contact stability.
FIG. 5 is a schematic view illustrating the exterior appearance of a prior art IC socket of this type, and FIG. 6 shows the details of the construction thereof. The IC socket 11 comprises a plastic housing 13 in which a number of probe pins 12 are carried. In the illustrated example, the IC socket 11 is adapted to accommodate CSPs (Chip Size Packages) such as BGA (Ball Grid Array) and has a grid array of several tens of probe pins 12. It is to be understood that in FIG. 5 the probe pins 12 are symbolized to illustrate only the positions of the array of the pins.
As shown in FIG. 6, each of the probe pins 12 comprises a metallic tube 14, a fixed plunger 15 integrally fixed to the tube at one end thereof, and a movable plunger 17 disposed at the opposite end and biased by a coil spring 16. A tube assembly 18 comprising the tube 14 and the fixed plunger 15 is held in place by the housing 13 and a bottom cover 21 with one end portion of the tube assembly accommodated in a through-aperture 19 formed through the housing 13 and the other end portion accommodated in a through-aperture 22 formed through the bottom cover 21. The bottom cover 21 is made of resin and is fastened to the housing 13 as by screws, not shown in FIG. 6.
The IC socket 11 is mounted on a socket board in use and devices to be tested are successively mounted on the IC socket in that state to be subjected to testing. FIG. 7 shows how the probe pin 12 works during the testing. Specifically, FIG. 7A shows the probe pin 12 before the IC socket 11 is mounted on the socket board 23; FIG. 7B shows the probe pin 12 after the IC 11 socket has been mounted on the socket board 23; and FIG. 7C shows the probe pin 12 when a device 24 to be tested is mounted on the IC socket 11.
When the IC socket 11 is mounted on the socket board 23, the movable plunger 17 of the probe pin 12 is urged upwardly by an electrode pad 25 on the socket board 23 as shown in FIG. 7B whereby the entire probe pin 12 is moved upward until stop means 14a formed on the outer periphery of the tube 14 comes into abutment against the interior wall 13a of the housing 13. Further urging by the electrode pad forces the movable plunger 17 into the tube to compress the coil spring 16, so that the movable plunger 17 and the electrode pad 25 are maintained in pressure contact by the restoring force of the coil spring 16.
FIG. 7C illustrates the device 24 to be tested as being a BGA having solder balls 24a as terminals. As the device 24 being tested is loaded on the IC socket 11, the solder ball 24a presses on the fixed plunger 15 whereby the tube assembly 18 is moved downwardly while the coil spring 16 is further compressed, so that the solder ball 24a and the fixed plunger 15 are maintained in pressure contact by the restoring force of the coil spring 16.
Upon completion of the testing, the device 24 being tested is removed whereupon the tube assembly 18 is moved upwardly back to the position shown in FIG. 7B.
As discussed above, it is to be noted that the conventional IC socket 11 is configured such that the tube assembly 18 is moved up and down as the device 24 being tested is removed from and mounted on the socket, respectively.
However, the thus constructed IC socket 1 has often encountered a situation in which the tube assembly 18 fails to return to its original position even though the device 24 under test has been removed. That is, there has often occurred the situation in which the tube assembly 18 remains pushed in so that when the next device 24 to be tested is loaded on the socket no good contact is established between the device and the socket.
Occurrence of such contact failure results in a test failure. If retesting is conducted to determine whether the test failure is due to failure of the device 24 being tested itself or to contact failure of the IC socket 11, it results in a marked increase in the average number of man-hours needed for testing. In addition, since even the retesting cannot insure that such failures distinguished one from the other, it leads to a deterioration in production. For this reason, the failure of the tube assembly 18 to return to its original position has become a serious problem.
Such failure of the tube assembly 18 to return to position arises from reduction in slidability of the tube 14. More specifically, the tube 14 is provided around its outer periphery with a stop projection 14a as described above. The stop projection 14a is formed by removing, by machining operation, the rest of the outer peripheral material of the miniature tube 14 made by a drawing process other than the stop projection 14a forming portion. Hence, the slide surfaces of the tube 14 are machined surfaces having rather poor surface roughness, so that those surfaces will scratch or abrade the opponent slide surfaces of the housing 13 and bottom cover 21 and produce wear debris which will accumulate in gaps between the tube 14 and the through-apertures 19, 22, resulting in poor slidability.
It is also to be noted that the tube 14 is configured so as to be positioned by both of the through-aperture 19 in the housing 13 and the through-aperture 22 in the bottom cover 21 for sliding movement along the aperture walls. Consequently, if there is some misalignment in assembly between the housing 13 and the bottom cover 21, for example and hence the opposing through-apertures 19 and 22 are out of alignment with each other, radial forces may be exerted on the tube 14 to impair the slidability of the tube, resulting in an increase in resistance to the sliding movement which in turn brings forth a situation in which wear debris is more likely to be produced.
Accordingly, it is an object of this invention to provide an IC socket which overcomes the aforesaid drawbacks to the prior art IC socket and which has a superior contact stability attended with no deterioration of slidability.
It is another object of this invention to provide an IC testing apparatus equipped with such IC sockets having a superior contact stability.
According to this invention, in an IC socket comprising a housing and a bottom cover integrally secured together, the housing and the bottom cover each having an array of through-apertures formed therethrough, the through-apertures in the housing and the associated through-apertures in the bottom cover being in opposing alignment with each other, and a probe pin being accommodated and held in each pair of the opposedly aligned through-apertures, each of the probe pins comprising: a tube assembly including a tube having a narrowed one end and a stop means in the form of a flange formed around the outer periphery of the tube intermediate its opposite ends and a fixed plunger fixedly fitted in the other end of the tube; a movable plunger having a base portion accommodated in the tube and restrained by the narrowed one end against axial dislocation therefrom and an extension extending from the base portion out through the narrowed one end and adapted to make pressure contact with a terminal of a device being tested; a first resilient member housed in the tube to urge the movable plunger in such a direction as to extend the plunger out of the narrowed one end; and a second resilient member surrounding the tube and interposed between the inner surface of the housing and the stop means, wherein the tube assembly is held in position with its opposite ends accommodated in the associated pair of opposedly aligned through-apertures, the stop means being urged by the second resilient member into abutment with the inner surface of the bottom cover whereby the forward end of the fixed plunger is projected beyond the outer surface of the bottom cover.
It is thus to be appreciated that the movable plunger is moved vertically up and down as the device being tested is removed from and mounted on the socket, respectively and that the movable plunger slides along the inner peripheral surface of the tube having a relatively low surface roughness so that good slidability is insured to provide for an IC socket having a superior contact stability.